Water-soluble liquid ink compositions have widely been employed in ink jet recording systems, but their use is limited to printing on special paper with a non-blotting coat due to their easy soaking through usual paper. Where the water-soluble liquid ink compositions are applied to OHP (overhead projector) sheets, the poor drying properties have made it necessary to give a special pretreatment to the sheet surface.
Under these circumstances, a hot-melt ink jet recording system has been proposed, which affords satisfactory print quality irrespective of the kind of paper. According to this system, a hot-melt ink composition mainly comprising a wax, etc. which is solid at room temperature is liquefied by heating, imagewise jetted onto paper by means of any energy, and cooled and solidified on the paper to form a dot image.
The hot-melt ink jet recording system has various advantages over the aqueous ink jet recording system in that the ink, as being solid at room temperature, causes no stains on handling; that evaporation of the ink in the molten state can be minimized, causing no clogging of a nozzle; and that the molten ink is rapidly solidified and dried immediately after being jetted, causing no blots on paper, so that various sorts of paper, such as Japanese paper, drawing paper, post cards, etc., may be used without requiring any pretreatment.
Comprising a wax as a main component, the conventional hot-melt inks have low transparency on an OHP sheet. In order to improve transparency, it has been proposed to smooth the surface of the ink image fixed on an OHP sheet by means of a hot roller to thereby prevent scattering of light. However, such a post treatment is still insufficient for obtaining desired transparency.
Thus, while the hot-melt ink jet recording system is expected to be applied to office automation equipment, printers for domestic use, facsimiles, etc. on account of its advantages over the aqueous ink jet recording system as mentioned above, the poor transparency of the hot-melt ink on an OHP sheet has been a hindrance to putting it to practical use.